1. Field of the Invention
The invention is generally related to optical scanning holography and, more particularly, to a system which requires only a two dimensional scan to record three dimensional information.
2. Background Description
A recent major innovation in light microscopy is the use of fluorescent dyes as selective stains or markers in living cells. These dyes were originally employed by biologists to improve contrast and resolution, and are now being used in conjunction with laser scanning and confocal microscopy techniques to obtain three-dimensional (3-D) images. The advantages of fluorescent techniques in light microscopy are well known. At magnification levels sufficiently high to image single cells clearly, most biological structures are colorless and transparent. In the absence of some mechanism to improve the contrast in such a specimen, important features may remain invisible. Traditionally, selective staining has been used to darken or color certain aspects of a specimen. However, as with the electron microscope, this type of specimen preparation frequently kills living cells. Fluorescence microscopy has been successful at marking features of living cells and thus improving resolution and specificity.
Currently, many of the principal 3-D microscopy techniques involve sectioning and reconstitution. The approach is to take a series of sections through the sample at different depths, image and then merge the information into a single, 3-D image. The required 3-D scan is the major drawback of these methods. The 3-D scanning process is time consuming and requires very precise mechanical positioning. In addition, an immense amount of data must be stored and manipulated in order to reconstruct the image numerically in three dimensions.
Holographic recording using an active optical heterodyne scanning technique was first suggested by Poon and Korpel in 1979 and subsequently analyzed by Poon in 1985. In recent years, real-time holography using an active optical heterodyne scanning technique for recording and electron-beam-addressed spatial light modulator-based reconstruction has been extensively studied and demonstrated. Recording and real-time reconstruction of two dimensional objects has been reported, and the 3-D imaging capability of the technique has been demonstrated.
U.S. Pat. 5,064,257 discloses an optical heterodyne scanning type device.